My neighbor moved out of her house about a two weeks ago and apparently there was a bearded dragon that had been left behind. He obviously wasn't being taken care of prior to this abandonment either because he's extremely thin, he had some sores on the underside of his tail and stomach, a few of his limbs look discoloured as well, and I'm certain he's dehydrated as well. I've moved him into a leaky aquarium that we have (using news paper as substrate because that seems like it'd be the cleanest and least irritating to the sores) and offered him food (some lettuce with a bit of banana) and water. He has yet to touch the food or water and I haven't been able to give him a good look over because he's too aggressive to handle. ):

I've never owned a bearded dragon before and only have a general idea of how to care for them but in the poor condition this guy's in, I'm kind of at a loss.
Does anyone have any tips or advice they can give me?